Fast shortest distance between two line segments (in N dimensions)

This function implements the fast algorithm proposed in Vladimir J. LUMELSKY, "On fast computation of distance between line segments," Information Processing Letters 21 (1985) 55-61. for computing the shortest distance between two line segments.
It handles all degenerate cases as well (when the lines are parallel, one line is a point, both lines are points).

Optionally, the function can return the closest two points on the line segments.